Nearly half of those who handle missile launch operations at the Malmstrom Air Force Base in Montana are now involved in the proficiency test scandal.

By Jim Miklaszewski, Courtney Kube and Elizabeth Chuck, NBC News

The number of nuclear missile launch officers under investigation for allegations of cheating has ballooned to 92, the Air Force said Thursday.

The new total is nearly three times the initial 34 officers who were implicated in the scandal and nearly one-fifth of the force. The officers have been taken off their missile wing duties during the investigation into the cheating, which happened during a key proficiency exam, Air Force Secretary Deborah Lee James said at a Pentagon news briefing.

Of the 92, 40 are suspected of actually cheating by obtaining answers in advance of the test; the remaining 52 were allegedly aware of the cheating, but failed to report it to superiors.

Officials have stressed that there has been no change in the overall nuclear mission and no degradation of the U.S. nuclear capability.

"This is a failure of integrity, not a failure of the mission," James said Thursday.

The original officers in the probe, all assigned to the 341st Missile Wing at Malmstrom Air Force Base in Montana, are accused of apparently texting answers to each other, or knew that the cheating was going on and didn't report it, according to officials.

The monthly exam tested the officers' knowledge of the missile launch systems. It was administered in August and September 2013.

Air Force Chief of Staff General Mark Welsh said earlier this month the officers shared the exam "electronically.” Text messages were involved, he said. He would not expand on the exact circumstances of the alleged cheating, citing an ongoing investigation.

The investigation into the cheating ring was announced on Jan. 15 by the Air Force.

The 341st Missile Wing provides security for 150 nuclear-armed Minuteman 3 intercontinental ballistic missiles, one third of the entire ICBM force. James said there is no evidence of similar cheating at the other two nuclear missile bases, F.E. Warren in Wyoming and Minot in North Dakota.

Just two days ago, a U.S. military official told NBC News the number of officers under allegations had nearly doubled.

James, who is the service's top civilian official, said Thursday that the systemic micromanagement in the nuclear force has created "undue stress and fear," and that situation at Malmstrom was "not a healthy environment."

She has said that the alleged cheating at Malmstrom was discovered during a previously announced probe of drug possession by 11 officers at several bases. Initially, that probe only included 10 officers.